billalhossainNumerical Analysis of Free Space Multiband Wire Antenna for GSM
Application
Name:Biswajit Barua(0709022) & Adnan Hossain Abin(0709014)
E-mail: biswajitbarua100@yahoo.com , abin_ece2k7@yahoo.com
Student of Dept. of Electronics and Communication Engineering
Khulna University of Engineering and Technology,Khulna-9203,Bangladesh
Abstract:
This project presents a triple band (i.e. centered at 900MHz, 1800MHz & 2100MHz) supported wire antenna which is applicable for mobile antenna & Wi-Max operation. This antenna is simulated in software named 4NEC2 in which the antenna is designed and different parameter is measured. For 900MHz centered frequency, this antenna supports a bandwidth of 64MHz from 868 MHz to 932 MHz. For 1800MHz centered frequency, this antenna supports a bandwidth of 88MHz from 1748 MHz to 1836 MHz. For 2100MHz centered frequency, this antenna supports a bandwidth of 22MHz from 2089 MHz to 2111 MHz. The impedance, Voltage standing wave ratio(VSWR), reflection
coefficient, gain and other parameter are perfectly simulated for this antenna which makes its performance better.
Keyword:
GSM based multiband wire antennas necessity and application.
Introduction:
Mobile phone networks are living through times of unprecedented growth in the subscriber base and the number of services being offered. At the same time operators are encountering growing pressures from planners and environmental groups. At present the industry needs smaller and less conspicuous based stations with reduced unit cost, all achieved with no compromise in performance.
The pressure on spectrum in the 900MHz band has led to the grant of license to operate in multiband such as 900MHz band, 1800MHz band, 2100MHz band. In some countries where 1800MHz operators have faced difficulties in providing sufficient coverage in less populated rural areas , some 900MHz spectrum has been made available to allow coverage to be extended at lower cost. 2100MHZ band spectrum is used in modern countries. This band is not supported in Bangladesh. When an operator is adding an additional band, the cost of implementation must be held to a minimum, and, the planning problems must be effectively managed. The effectiveness of the existing network must not be compromised.
In general, where the operator is adding a new frequency band to an existing network, the most important consideration is to maintain the same performance in the existing band. Some compromise may be acceptable on the newly introduced band. This is especially true where the new band is to be introduced to increase capacity for existing network services. Where the objective of the operator is to overlay a new network carrying alternative services, the antenna requirement is different, as closely matched coverage may be more important.
However, these frequency band spectrums are also used in wireless local area network (WLAN) & Worldwide Interoperability for Microwave Access (WIMAX) application.
Antenna structure:
The antenna is made of a combination of F-shaped & L-shaped structure. Total length of wire used in this antenna, is 42.358cm which is small compared to any other wire antenna structure. This antenna is constructed in xz pane. So it stands vertically with its y plane. It is so stable with its feeding or sma connector because its small structure.
- Multiband wire antenna structure,Multiband antenna structure in 4NEC2,simulated radiation pattern
In this graph, the voltage standing wave ratios are 1.078 at 900MHz frequency, 1.103 at 1800MHz frequency & 1.073 at 2100 MHz frequency. These values are constant for a small range of their individual frequency spectrum. In these frequency ranges, antenna radiates most highly.
simulation result
simulation result1
The value of reflection coefficient in this antenna are -28.5db for 900MHz, -26.2db for 1800MHz & -29.1db for 2100MHz. it is much greater than the standard value. So performance is much better in this case.The gain of any antenna is inversely proportional to the bandwidth of the antenna. For 900MHz band, the bandwidth of the antenna is 64MHz. so the value of gain is certainly increased to 1.54 which is greater than the standard value. But this gain is decreased in 1800MHz band with a 88MHz bandwidth.The impedance of this antenna are 47.41 ohm, 50.2ohm & 50.25 ohm for 900MHz, 1800MHz & 2100MHz band which is nearly equal to the its standard value 50 ohm. So this antenna reduces its power loss and gives maximum radiation in free space.
Measured Result:
This antenna is made of three frequency band spectrum i.e. 900MHz band, 1800MHz & 2100 MHz. But in these frequency spectrum is not supported in the laboratory for the measurement of performance. Only two frequency spectrums are supported in laboratory. That is 914MHz & 2450MHz. We consider the 914MHz for the measurement as nearest value of 900MHz band. Few performance parameters may fluctuate from the simulation result.The radiation pattern is almost circular. It can be changed with some parameter. If there are no obstacles in the certain range of its radiation, then it gives more circular and accurate radiation pattern. If there are obstacles, the radiation pattern would be distorted. Radiation pattern also depends upon its position of radiation. Some antenna radiates properly at vertical position and some at horizontal.
experimental result
The measured value of voltage standing wave ratio for incident wave is different from simulated value. The value of VSWR at 0dB is 1.0130. it is increased at -4dB & -8dB respectively. The value at that level is 1.0355 & 1.1250 which is larger than the simulated value.
1.0001. it is increased at -4dB & -8dB respectively. The value at that level is 1.0282& 1.0513. which is larger than the simulated value.
| Wire NO |
segment |
Radius |
|
1 |
2 |
1.026mm |
|
2 |
8 |
1.026mm |
|
3 |
2 |
1.026mm |
|
4 |
1 |
1.026mm |
|
5 |
1 |
1.026mm |
|
6 |
1 |
1.026mm |
|
7 |
2 |
1.026mm |
|
8 |
9 |
1.026mm |
|
9 |
3 |
1.026mm |
|
10 |
9 |
1.026mm |
|
11 |
5 |
1.026mm |
|
12 |
8 |
1.026mm |
|
13 |
1 |
1.026mm |
Table: wire segment and radius for all wires
The wire used in this antenna, is made by copper. The radius of this wire is 1.026mm which is usually known as 12 gauges wire. The antenna fading is given at wire number five which length is 1.2cm and the antenna fading is in the middle of that wire.
Conclusion:
The main objective of designing this triple band antenna is to omit the band limitation problem in mobile phone network. This antenna is designed in software named 4NEC2. So all parameter should be maintained. In 4NEC2, it is made at x-z axis. So it works better in its vertical position rather than horizontal position. The major limitation of this antenna is gain which can be reduced by changing its parameter. Such as micro strip antenna gives more gain than wire antenna. So in modern world it is used more because of its performance. But wire antenna are also used for its low cost and simplicity.
Reference:
[1]. Khaled Mahbub Morshed, Debabrata Kumar Kormokar and Abu Md. Numan-Al-Mobin ‘Numerical analysis of impedance matched Inverted-L antennas for Wi-Fi operations’ , proceeding of 2009 12th ICCIT, 2009, Dhaka , Bangladesh.
[2]. Kheya Banerjee, Abu Md. Numan-Al-Mobin and Khaled Mahbub Morshed ‘ A Compact Loop Type Antenna for Millimeter Band Applications’ proceeding of 2009 12th ICCIT, 2009, Dhaka , Bangladesh.
[3]. http://www.lemosint.com/radiometrix/radiometrix_details.php?itemID=216
[4]. http://cellphonesafety.wordpress.com/category/914-mhz/
[5]. Antenna & wave propagation-K.D. Prasad
[6]. Antenna theory-Balanis
[7]. Internet.
[8]. Wikipidia
[9]. Encyclopedia
Project 4 Science Fair 